The biological basis for the development of benign proliferative disease (benign prostatic hypertrophy, BPH) in the prostate is poorly understood. Recent data from our laboratory shows that the CXC-type chemokine, CXCL12, is secreted by aging prostate stroma and stimulates the proliferation of both non-transformed and transformed prostate epithelial cells. Moreover, the CXCL12-mediated proliferative responses are ERK- dependent in non-transformed prostate epithelial cells, but ERK-Independent in transformed cells. We now propose that inactivation of PTEN may be the critical factor that modulates downstream signaling and the specific CXCL12-stimulated proliferative responses of non-transformed and transformed prostate epithelial cells. Preliminary data presented here shows that the CXCL12-mediated proliferative response requires EGFR, and that CXCL12 activation of ADAMs may catalyze CXCR4-mediated transactivation of EGFR. Supporting immunohistochemical analysis of human prostate tissues show that CXCL12 and CXCR4 are expressed in benign and malignant proliferative diseases of the prostate;that activated Akt has been directly correlated, and activated ERK inversely correlated, with a high proliferative index in human prostate tumors, and that Akt activation has been identified as an excellent predictor of poor clinical outcome in prostate cancer. Based on these data, we hypothesize that the CXCL12/CXCR4 axis can `switch'between activating the Raf/MEK/ERK and PI3K/PTEN/Akt pathways to promote cellular proliferation, and that the pathway `choice'depends on PTEN status. We propose to test this hypothesis through the accomplishment of three Specific Aims: SPECIFIC AIM 1: Determine whether the signaling mechanisms activated or inhibited by CXCL12 that promote cellular proliferation in non-transformed human prostate epithelial cells are PTEN-dependent. SPECIFIC AIM 2: Determine whether the CXCL12-stimulated proliferative response is EGFR- dependent. SPECIFIC AIM 3: Determine whether the protein expression of CXCL12, its receptor, and downstream effectors correlate with benign proliferative disease in aging human prostate tissues. Significance of the Proposed Research: Our preliminary data shows that CXCL12 stimulates aging- associated cellular proliferation, but utilizes different intracellular signaling mechanisms to mediate these responses in non-transformed versus transformed prostate epithelial cells. The elucidation of these mechanisms will have significant consequences for the development of therapeutics targeted against CXCL12 activity to efficaciously treat benign proliferative (BPH) versus malignant proliferative (PCa) disease in the prostate. PUBLIC HEALTH RELEVANCE: Our preliminary data shows that the chemokine CXCL12 stimulates aging-associated cellular proliferation, but utilizes different intracellular signaling mechanisms to mediate these responses in non-transformed versus transformed prostate epithelial cells. The elucidation of these mechanisms will have significant consequences for the development of therapeutics targeted against CXCL12 activity to efficaciously treat benign proliferative (BPH) versus malignant proliferative (PCa) disease in the prostate.